In a conventional chuck device as disclosed in Patent Document 1, a rotary sleeve provided to a main body is rotated, and by the rotation of a rotary nut which rotates together with the rotary sleeve, jaws which are screwed together with the rotary nut are expanded, contracted, and slid, and a tool is gripped by the jaws.
Known structures for preventing disengagement between the rotary nut or the main body and the rotary sleeve in such a chuck device include a structure such as the one disclosed in Patent Document 1, for example, in which a C-shaped stop ring (retaining ring) is placed in a groove provided to the internal peripheral surface of the proximal end side of the rotary sleeve, and the (shape-retaining ring for retaining the shape of the) rotary nut is engaged in the stop ring and retained; and a structure such as the one disclosed in Patent Document 2, in which a stop ring the same as the one described above is placed in a groove provided to the internal peripheral surface of a distal-end opening of a rotary sleeve (external cover part) in which jaws retract, and the main body (chuck body) is engaged in the stop ring and retained. The rotary nut is annular and fitted in the main body, and disengagement of the rotary sleeve is prevented by retaining either the rotary nut or the main body.